The present invention relates to methods of manufacturing glass articles and molding containers for use in the methods and, more particularly, to a method of manufacturing a glass article by means of a sol-gel process using a metal alkoxide, and a molding container for use in the method.
As a method of manufacturing a glass article, a melting process is known in which a glass row material containing SiO.sub.2 as a major component and other metal oxides such as Al.sub.2 O.sub.3, TiO.sub.2, PbO and so on as optional components is melted to obtain the glass article. Further, a sol-gel process is also known in which a metal alkoxide expressed by a general formula M(OR).sub.n is used to obtain a glass article. In the general formula, M represents metals such as Si, Al, Ti, Pb and the like, R represents an alkyl radical, and n represents integers corresponding respectively to valences of the respective metals.
The sol-gel process using the metal alkoxide is as follows. That is, the metal alkoxide is added into and mixed with an organic solvent such as ethanol or the like. Subsequently, water and hydrolysis catalyst are added to the mixture to obtain a homogeneous sol solution. Then, the sol solution is hydrolyzed, dehydrated and condensed to obtain a wet gel. The wet gel is dried and shrunk within a molding container to form a dry gel. Subsequently, the dry gel is heated and sintered into a non-porous glass. Thus, the desired glass article is obtained.
The sol-gel process has such advantages that the glass article having high purity can be obtained, the glass article can be obtained at considerably lower temperature than the conventional melting process, and so on. Accordingly, in recent years, the spotlight of attention is focused particularly on the sol-gel process. The sol-gel process has already been put into practice in manufacturing of a fibrous glass article, manufacturing of a coating film, and the like.
By the way, as represented by a photomask substrate, there are many demands for a glass article in the form of a planar plate. It has been desired to establish a manufacturing method of the glass article in the form of a planar plate, particularly, a large size glass article in the form of a planar plate by the sol-gel process using the metal alkoxide.
In the case where the large size glass article in the form of a planar plate is attempted to be manufactured by means of the sol-gel process which has conventionally been tried, however, there is such a problem that cracks tend to occur when the wet gel is dried and shrunk within the molding container to obtain the dry gel. Thus, it has extremely been difficult to efficiently obtain the large size glass article in the form of a planar plate. For this reason, in order to efficiently obtain the large size glass article in the form of a planar plate by means of the sol-gel process using the metal alkoxide, there is such a problem that the cracks must be restrained which occur when the wet gel is dried and shrunk within the molding container to form the dry gel.